Re: pg_trgm version 1.2

See Tom Lane's comment about downgrade scripts. I think just remove it is a right solution.

Let's consider '^(?!.*def).*abc' regular expression as an example. It matches strings which contains 'abc' and don't contains 'def'.

# SELECT 'abc' ~ '^(?!.*def).*abc';

 ?column?

----------

 t

(1 row)

# SELECT 'def abc' ~ '^(?!.*def).*abc';

 ?column?

----------

 f

(1 row)

# SELECT 'abc def' ~ '^(?!.*def).*abc';

 ?column?

----------

 f

(1 row)

Theoretically, our trigram regex processing could support negative matching of 'def' trigram, i.e. trigramsMatchGraph(abc = true, def = false) = true but trigramsMatchGraph(abc = true, def = true) = false. Actually, it doesn't because trigramsMatchGraph() implements a monotonic function. I just think it should be stated explicitly.